Integrins are heterodimeric cell surface receptors involved in the regulation of cellular adhesion and cell-cell interactions. As such they play a critical role in many biological processes of importance to human health. The goal of our proposed research effort is to provide the first quantitative understanding of role of the membrane and its lipid composition on the mechanism of integrin activation and signaling. We use a novel approach by employing Nanodiscs, homogeneous self- assembled nanometer scale discoidal bilayers to provide precise control of the membrane composition. We couple this experimental approach with molecular dynamic simulations employing a novel membrane mimetic that allows enhanced sampling at an atomic resolution, thereby a detailed description of the interactions occurring at the protein-membrane interface. By focusing our experimental and theoretical thrusts on talin, a key activator of integrin involved in inside-out signaling, we answr questions as to how talin engages the membrane and how the presence of anionic phospholipids, in particular PIP2, regulates this important interaction. In addition, we dissect th mechanism of talin activation from its auto-inhibited form separating the contributions from interactions with phospholipids, and that of the effectors Rap1, RIAM, and PIPKgamma. Through this integrated research plan we seek to understand how the sum of these interactions regulates the activation of integrin and control its affinity for ligand binding. PUBLIC HEALTH RELEVANCE: Integrins are an important class of adhesion receptors that are involved in a wide range of biological processes including embryonic development, hemostasis, cell migration, wound healing, and the immune response and their impaired function has been linked to key human diseases such as arthritis, heart attack, stroke, and cancer. This project seeks to investigate the role of the membrane surface in the formation of active integrin complexes with primary focus on the adapter protein talin. Employing a closely coupled set of theoretical and experimental biophysical techniques, the goal is to present a detailed structural view for activation of integrin on a membrane surface.